Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

tcp_bpf: Fix the sk_mem_uncharge logic in tcp_bpf_sendmsg

The current sk memory accounting logic in __SK_REDIRECT is pre-uncharging tosend bytes, which is either msg->sg.size or a smaller value apply_bytes.

Potential problems with this strategy are as follows:

- If the actual sent bytes are smaller than tosend, we need to charge some bytes back, as in line 487, which is okay but seems not clean.

- When tosend is set to apply_bytes, as in line 417, and (ret < 0), we may miss uncharging (msg->sg.size - apply_bytes) bytes.

[...] 415 tosend = msg->sg.size; 416 if (psock->apply_bytes && psock->apply_bytes < tosend) 417 tosend = psock->apply_bytes; [...] 443 sk_msg_return(sk, msg, tosend); 444 release_sock(sk); 446 origsize = msg->sg.size; 447 ret = tcp_bpf_sendmsg_redir(sk_redir, redir_ingress, 448 msg, tosend, flags); 449 sent = origsize - msg->sg.size; [...] 454 lock_sock(sk); 455 if (unlikely(ret < 0)) { 456 int free = sk_msg_free_nocharge(sk, msg); 458 if (!cork) 459 *copied -= free; 460 } [...] 487 if (eval == __SK_REDIRECT) 488 sk_mem_charge(sk, tosend - sent); [...]

When running the selftest test_txmsg_redir_wait_sndmem with txmsg_apply, the following warning will be reported:

------------[ cut here ]------------ WARNING: CPU: 6 PID: 57 at net/ipv4/af_inet.c:156 inet_sock_destruct+0x190/0x1a0 Modules linked in: CPU: 6 UID: 0 PID: 57 Comm: kworker/6:0 Not…